The Confluence Cloud environment does not currently support user macros, although templates are supported.

User macros provide a way for the customer to insert custom HTML and JavaScript, which due to the security model of Cloud (where Atlassian uses the same web interface for system administration), is actually a security vulnerability due to the possibility of cross-site attacks by malicious customers against our administrative accounts.

https://confluence.atlassian.com/confcloud/restricted-functions-in-confluence-cloud-734070955.html

User macros allow HTML and JavaScript to run in Confluence Cloud, which can affect performance. To see what custom macros can be added to Confluence Cloud, check out the Atlassian Marketplace. Note: To install any of the Confluence Cloud macro apps, you must be the administrator for the Atlassian Cloud site.

Would it be possible to support simple user macros in Cloud, that operate like a template (i.e. layout, content, supported macros) but are called by a user-defined macro instead?